Background and objective <p>Older emergency patients are at a higher risk of mortality, hospitalization, readmission, and functional decline. However, the potential factors for these adverse health outcomes in the Chinese population have not been extensively explored. Our study aims to investigate the prevalence and development of adverse health outcomes among older emergency patients, explore the risk factors, and offer insights for clinical decisions.</p> Methods <p>This prospective cohort study enrolled 1,023 patients aged ≥ 65 from a Chinese tertiary hospital emergency department (March-July 2023). Logistic regression analyzed predictors of 90-day functional decline and/or mortality.</p> Results <p>After 90&#xa0;days of visiting the emergency department, 60.2% of older patients experienced functional decline and/or mortality. High-risk patients (8.5%) identified by the APOP screener exhibited sustained functional decline. We grouped major risk factors into three categories. Sociodemographic: Advanced age (<i>OR</i> = 1.053 for functional decline), male gender (<i>OR</i> = 1.411 for hospitalization), and BMI &lt; 18.5 (O<i>R</i> = 3.040 for mortality). Clinical factors: acuity triage level (<i>OR</i> = 4.206 for composite outcomes), arrival by ambulance (<i>OR</i> = 3.354 for mortality), and Charlson Comorbidity Index (<i>OR</i> = 2.912 for composite outcomes). Geriatric assessments: impaired cognition (<i>OR</i> = 1.814 for functional decline) and number of medications (<i>OR</i> = 3.319–3.554 for ED revisits) (<i>P</i> &lt; 0.05).</p> Conclusions <p>Adverse outcomes, including functional decline and even mortality, are prevalent among older emergency patients in China, especially those classified as high-risk by the APOP screener. These findings highlight the imperative of incorporating risk assessment tools into routine triage and prioritizing multidisciplinary interventions for high-risk subgroups.</p>